Which servers is the Verizon account using? If they are pop.aol.com and smtp.aol.com, it should be sufficient to change the authentication on both to OAuth2. If they are pop.verizon.net and smtp.verizon.net, an app password is required.

https://support.mozilla.org/en-US/questions/1344702

mine are verizon.net. Been using for YEARS. Something happened.

AOL changed their authentication standards so 'normal password' with the account password is replaced by an app password or OAuth2, which is now standard for gmail and Yahoo accounts.

That was years ago, Always use normal password. I tried changing auth to OAuth2, didn't work. Said not allowed or whatever

If you keep the authentication as normal password, you must use an app password in place of the account password, as explained in the link in my first reply.

OK,I did that app password and saved. It works. Please tell me why this suddenly happened? LONG time TB user and verizon email

AOL enforced OAuth2/app passwords a year or two ago, and apparently Verizon users were notified in the last few months. There are plenty of posts in this forum about the change for Verizon, but I'm not a customer so can't be more specific.

Obv I didn't get that notification last few months. Always had normal pw, and the OAuth2 did not work when I tried

If you change the servers to pop.aol.com and smtp.aol.com, with OAuth2 and your @verizon.net account, it might work. Try it if you like in a new profile created from Help/More Troubleshooting, about:profiles.